Solid state millimeter wave sources have generally relied on power combining to achieve useful power levels (>milliwatts). Printed circuit or waveguide combining is typically used at lower frequencies (e.g.)<75 Ghz). At higher frequencies, however, these method are either very inefficient due to high losses, or are difficult to fabricate due to tight mechanical tolerances.
Free space combining, also called “quasi optical” combining, eliminates the latter problem by allowing electromagnetic energy to combine in free space. Quasi optical approaches have been know to provide higher efficiency by utilizing free space combining, but solid state devices cannot produce much power above 100 Ghz. Frequency triplers have been used to produce high frequency power, even in array form, but such “quasi optical” approaches have not utilized monolithic integration of triplers with power amplifiers in array form. One reason this has not been attempted is the tight array spacing at 3f0 severely restricts the available real estate for the received antennas, amplifier, and tripler circuitry. Standard array approaches require the radiating elements at 3f0 to be closely spaced (nine per unit cell) to avoid grating lobes. At high frequencies, there is insufficient real estate to fit all of the required circuitry together with the antenna elements on a monolithic device.
The availability of high power at high frequencies may be useful in communications above 100 GHz range, directed energy beams, room temperature submillimeter wave imaging, chemical and biological sensing, and high angular resolution and compact radar. Other applications may include for example, concealed weapons detection, driver vision assist in fog, landing aid for aircraft and helicopters, biological and chemical agents detection, missile seeker radar, and remote sensing. Other implementations are possible.
Thus, there is need for a compact high power high frequency source.